The Speedlite 600EX-RT is engineered to provide a level of performance and reliable, professional flash photography when combined with advanced Canon SLR models.Features include wireless two-way radio communication for reliable radio triggering, an expanded zoom range and a higher guide number. The improved hot shoe contacts and flash head durability are enhanced with an improved dust and water seal. The included color filter holder allows attachment of color correction filters to balance multiple light sources, or for creative color options.Wireless Control of Multiple Flash Units The Speedlite 600EX-RT features both traditional optical wireless transmission and radio controlled two-way wireless transmission. With a range of 98.4’ and 2.4 GHz frequency communication, the Speedlite 600EX-RT eliminates the directional limitations of optical transmitters, and can trigger up to fifteen remote Speedlites divided in to five groups. Choose automatic or manual settings of fifteen total transmission channels. Radio transmission IDs can be set to prevent misfiring in the event of same channel signal interference.20-200mm Zoom Range and Improved Guide NumberThe Speedlite 600EX-RT offers a 20-200mm zoom range, which expands to 14mm when the wide panel is used. The improved guide number of 197 ft. (60m) at ISO 100 expands creative lighting options and possibilities with the Speedlite 600EX-RT. In order to maximize power and minimize energy consumption, the Speedlite 600EX-RT can be directed to zoom in accordance with full-frame, APS-H and APS-C sensor sizes, depending on the camera being used.Improved Durability plus Dust and Water ResistanceThe design and construction standards of the Speedlite 600EX-RT are similar to the high end Canon SLR models, creating the most rugged, durable and reliable Speedlite available. The redesigned hot shoe contact ensures seamless communication between the flash and camera, plus improved dust and water resistant seals allow the Speedlite 600EX-RT to be used in most enviroments.AF Assist Beam Compatible with 61-Point High Density Reticular AFWorking in conjunction with EOS SLR cameras and lenses 28mm and longer, the Speedlite 600EX-RT automatically utilizes a built-in AF assist beam, designed for faster and more accurate autofocus even in dark or low contrast situations. Compatibility with the 61-Point High Density Reticular AF found in the EOS-1D X and the EOS 5D Mark III models is also featured.Dot-Matrix LCD panel and Backlight OptionThe Speedlite 600EX-RT has a 172 x 104 dot matrix LCD panel which displays flash status, wireless configuration plus other flash settings. The improved panel displays more detailed information than on previous models, and can be backlit at the touch of button when operating in low light conditions.Custom Functions for Creative FlexibilityThe Speedlite 600EX-RT features eighteen custom functions to accommodate any number of shooting styles. Features include flash exposure bracketing controls, modeling flash, test firing controls, AF assist control, power and energy saving features, beep and more. Personal functions can also be easily set, such as LCD panel illumination color and Master/Slave configurations.Full Swivel and 180 Degree RotationThe Speedlite 600EX-RT's flash head is designed for easy bounce flash in any direction. The head can be angled at 90 degrees up, 7 degrees down and rotated 180 degrees left and right. A bounce lock with release button helps to keep a set angle in place, allowing for continuos shooting. When the flash head is positioned front and up at 90 degrees, the Speedlite 600EX-RT features a panel to create a catch light in the subject's eyes for a more expressive look.